connection reset problem

hi:

I have a very strange problem and would like to ask you for help.

I am using redhat 7.2, and the usage of ssh is ok. Then I installed
nessus.

Now, I can use ssh to connect to other unix machines. however, after some
time (say a few minutes), I got "Connection reset by peer".
Connection to machine closed.

This happens if I do not type character in the terminal. However, if I
keep having some actions in this terminal, it seems fine.

What is wrong here?

thanks for your help

bo